Generally, a variety of casters are provided to have devices stopping the movements of wheels or retractably moving the wheels so as to conveniently move a teaching aid or a piece of furniture and to keep and utilize the teaching aid or the piece of furniture at the moving state to a given place.
One of conventional casters having a device stopping the movement of a wheel is disclosed in Korean Patent No. 10-0340292 (Dated Jun. 12, 2002) entitled ‘chair caster’, wherein the chair casters having rotation legs extended from the underside of a seat part in a multiple direction, rotation supports for adjusting heights between the seat part and the rotation legs, and a plurality of wheels disposed on the lower ends of the rotation legs, the chair casters include pinion members disposed inside the wheels, connection rods accommodated into the rotation supports and the rotation legs in such a manner as to move up and down and having the lower ends protruding outwardly from the lower portions of the rotation legs in such a manner as to be coupled or separated correspondingly to or from one sides of the pinion members to control the rotation of the wheels, bases disposed at a given height in the interiors of the rotation supports to guide the connection rods so that the top ends of the connection rods pass therethrough to a given height, springs disposed between the undersides of the bases and one sides of the connection rods to apply elastic forces to the connection rods so that the connection rods move down, and operating levers coupled to the top ends of the connection rods protruding upwardly from the bases by means of hinge pins and having one side ends protruding outwardly through the rotation supports to move the connection rods up.
According to the conventional chair casters, the wheels disposed on the rotation legs stop at the same time or individually in accordance with the operating positions of the operating levers, thereby preventing the casters from moving due to the wheels. However, in the state where a load is applied after a user sits on the seat part, it is hard to manipulate the chair casters, and the chair casters are very complicated in configuration to raise the manufacturing cost and lower the assemblability.
Further, one of conventional casters having a device stopping the rotation of a wheel is disclosed in Korean Patent Application Laid-open No. 10-2010-0022886 (Dated Mar. 3, 2010) entitled ‘device for automatically fixing rotation of wheel’, and the device includes: a wheel support for radially surrounding a portion of a wheel having a rotary shaft disposed at the center thereof and connected to the rotary shaft of the wheel; a moving part for surrounding the wheel support in such a manner as to be connected to the rotary shaft to move by a given distance up and down with respect to the wheel and the wheel support and having a fixing member disposed on one side thereof above the wheel so as to stop the rotation of the wheel upon the downward movement of the moving part; and an elastic body inserted into a guide column disposed on the top end of the moving part and the top end of the wheel support, wherein a rotatable linear rotary pin is disposed above the top end of the guide column by a given height in such a manner as to pass through a leg, and the rotary pin has a long or oval stopper fixed in the interior of the hollow leg.
According to the conventional device for automatically fixing the rotation of the wheel, if a load is applied to the hollow leg connected to the top end of the moving part, the moving part moves down to allow the fixing member to come into contact with the wheel, thereby automatically fixing the rotation of the wheel, and if the load applied to the leg is removed, the moving part moves up by means of the restoring force of the elastic body to allow the fixing member to be separated from the wheel, thereby rotating the wheel. Accordingly, the stopper fixed to the rotary pin rotates to pressurize the top end of the guide column formed on the top of the wheel support, so that the upward movement of the wheel stops to cause the wheel to be movable. That is, if the load is applied, the rotation of the wheel stops, and if the load is removed, the wheel is movable, thereby improving the conveniences in use. As the wheel does not move in the state where the load is applied, the operation of the guide column stops through the rotation of the stopper, but since there is no device for fixing the rotary pin operating the stopper, the stopper easily rotates even if small vibrations and impacts are generated, so that the wheel moves up and comes into contact with the fixing member, thereby undersirably stopping the rotation of the wheel.
Furthermore, one of conventional casters having a device moving and stopping a wheel through the retraction of the wheel is disclosed in Korean Patent Application Laid-open No. 10-2008-0015242 (Dated Feb. 19, 2008) entitled ‘rotation caster installed on moving object’, and the rotation caster includes a wheel eccentrically disposed on a wheel installation member, a moving object-attaching member shaft-coupled to the wheel installation member, while a ball bearing being disposed between the wheel installation member and the moving object-attaching member, a cylindrical portion formed in the moving object-attaching member, a post installed on the outer peripheral surface of the cylindrical portion, and an adjusting part having a screw portion formed on the outer peripheral surface of the cylindrical portion and a screw portion formed on the inner peripheral surface of the post so as to adjust an installation height of the post between the cylindrical portion and the post.
According to the conventional rotation caster installed on a moving object, when the cylindrical post or the height adjusting nut rotates to move the installation position of the post up and down, the wheel enters the post or protrudes outwardly from the post, so that it stops or moves. If a load is applied, however, it is very hard to artificially manipulate the cylindrical post or the height adjusting nut.
Also, another conventional caster having a device moving and stopping a wheel through the retraction of the wheel is disclosed in Korean Patent Application Laid-open No. 10-2005-0114596 (Dated Dec. 6, 2005) entitled ‘retractable caster’, and the retractable caster includes a housing having a moving hole penetrated on the lower portion thereof, the moving hole having a stepped projection formed therealong, a moving piece lockedly mounted selectively on the stepped projection, moved up and down along the moving hole, and elastically installed downwardly in the housing by means of a spring, a caster disposed on the lower portion of the moving piece, and stopping means disposed on the housing and the moving piece to restrict the upward and downward movements of the caster. Further, the stopping means has a stopping groove formed on the outer peripheral surface of the moving piece and a stopper elastically disposed on a coupling hole formed on the housing and adjusted at angle by means of a pin in such a manner as to be selectively stopped to the stopping groove.
According to the conventional retractable caster, the elastic force of the spring is used when the wheel enters a post or is retracted to the outside from the post. If a load is applied, the wheel enters the post, and contrarily, if the load is removed, the wheel protrudes outwardly from the post, thereby improving the conveniences in use. However, if a load itself is heavy or a load is applied additionally, the wheel enters the post, thereby making it impossible to move the wheel. So as to prevent the wheel from stopping, the locking state of the stopper maintaining the outwardly protruding state of the wheel from the post should be released to stop the upward movement of the moving piece or to allow the wheel to enter the post to stop the movement of the wheel. At this time, the free end of the stopper protruding outwardly from the post is compressed through an artificial force applied from a user's finger to cause the stopper to rotate around the pin, and accordingly, the contacted portion of the stopper with the moving piece is rotated and deviated from the moving piece, thereby releasing the locking state of the stopper. However, it is very hard to release the locking state of the stopper just by means of the rotation of the stopper caused only by the compression force of the user's finger in the state where the load is collected to the stopper contacted with the moving piece.